The objective of the proposed research is to increase our understanding of the way nervous systems are organized, by relating the network properties of a group of neurons to the physiology of the synaptic junctions which interconnect them. Synaptic neurophysiology and interneuronal organization will be correlated by examining the buccal ganglia of the marine mollusc Aplysia californica. This preparation contains a reference population of 30 cells, including 4 multiaction interneurons, which is analyzable at the level of the individual identified neuron, of the synaptic connections between individual identified cells, and of the cell networks formed by identified synapses. Electroanatomical identification of additional neurons, simultaneous intracellular recordings from pre- and post-synaptic elements, and voltage-clamping of post-synaptic potentials may yield answers to such questions as: How do direct excitation and disinhibition interact? Do anticholinesterases directly modify synaptic channel lifetime? do breakdown products of a neurotransmitter themselves cause postsynaptic conductance changes? The principles of organization of identified cell networks in this preparation may prove applicable to the experimentally less accessible populations of vertebrate neurons.